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Rotary ultrasonic machining is one of the nontraditional machining processes for advanced ceramics. Currently available in literature are publications on theoretical and experimental studies on material removal rates in rotary ultrasonic machining. However, there is no report on the systematic study of the cutting force in rotary ultrasonic machining. Furthermore, the effects of some process parameters on material removal rates and surface roughness have not been reported. This paper presents the results of designed experiments on rotary ultrasonic machining of a ceramic material (92% alumina). The designed experiments have revealed the main effects as well as the interaction effects of the process parameters (spindle speed, ultrasonic power, feedrate and grit size) on cutting force, material removal rate, and surface roughness.

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The enhancement of electron−phonon interaction provides a reasonable explanation for gate-tunable phonon properties in some semiconductors where multiple inequivalent valleys are simultaneously occupied upon charge doping, especially in few-layer transition metal dichalcogenides (TMDs). In this work, we report var der Waals epitaxy of 2H-MoSe 2 by molecular beam epitaxy (MBE) and gate-tunable phonon properties in monolayer and bilayer MoSe 2 . In monolayer MoSe 2 , we find that out-of-plane phonon mode A 1g exhibits a strong softening and shifting toward lower wavenumbers at a high electron doping level, while in-plane phonon mode E 2g 1 remains unchanged. The softening and shifting of the out-of-plane phonon mode could be attributed to the increase of electron−phonon interaction and the simultaneous occupation of electrons in multiple inequivalent valleys. In bilayer MoSe 2 , no corresponding changes of phonon modes are detected at the same doping level, which could originate from the occupation of electrons only in single valleys upon high electron doping. This study demonstrates electrostatically enhanced electron−phonon interaction in monolayer MoSe 2 and clarifies the relevance between occupation of multiple valleys and phonon properties by comparing Raman spectra of monolayer and bilayer MoSe 2 at different doping levels.

ζ -phase manganese nitride films were directly grown on sapphire substrates using plasma-assisted molecular beam epitaxy. Mn2N1.06, Mn2N0.98, and Mn2N0.86 films were synthesized by controlling the temperature of the effusion cell filled with highly pure manganese powder. The composition, structure, and morphology of the films were identified by x-ray photoelectron spectroscopy, x-ray diffraction and atomic force microscopy, and the magnetic properties of the films were characterized by a superconducting quantum interference device magnetometer at 5 and 300 K. The magnetic measurements reveal that Mn2N1±x exhibits weak ferromagnetism at 5 K, which is mainly ascribed to the weak interaction among the Mn cations induced by the nitrogen vacancies. Furthermore, the Mn2N0.86 single-crystalline films are found to have room-temperature ferromagnetism, which is attributed to the strain of the Mn2N0.86 films raised from lattice mismatch between the Mn2N0.86 films and the substrates.